Copper complexes oxygenation

Related to copper-containing enzymes such as laccase and tyrosinase, recent studies have been conducted on the structural characterization of the reactive species generated from molecular oxygen and copper complexes. A continuous effort has also been directed toward the efficient utilization of such oxygen-copper complexes as oxidants, in industrial processes, which will hopefully replace metal compounds such as chromate, manganate and others. 

A substantial fraction of the named enzymes are oxido-reductases, responsible for shuttling electrons along metabolic pathways that reduce carbon dioxide to sugar (in the case of plants), or reduce oxygen to water (in the case of mammals). The oxido-reductases that drive these processes involve a small set of redox active cofactors , that is, small chemical groups that gain or lose electrons. These cofactors include iron porjDhyrins, iron-sulfur clusters and copper complexes as well as organic species that are ET active. 

Copper and brasses in the systems are more resistant to corrosion because of a stable oxide film however, if ammonia is present together with oxygen, corrosion of copper and copper oxide rapidly occurs. The corrosion is an oxidation process and results in the formation of the ammonia-copper complex [Cu(NH3)42+], Corrosion of nickel and zinc components also may occur in like fashion. 

Kensler, T.W. and Trush, M.A, (1983). Inhibition of oxygen radical metabolism in phorbol ester-activated polymorphonuclear leukocytes by an antitumor promoting copper complex with superoxide dismutase-mimetic activity. Biochem. Pharmacol. 32, 3485-3487. 

X-ray crystallographic data has become available on the commercially important 1 1 copper complex azo dyes. The symmetrical dihydroxyazo ligand (16) forms the 1 1 square planar complex (17).13 A pyridine molecule occupies the fourth coordination site since this complex facilitated the formation of crystals suitable for X-ray diffraction. The complex (17) actually exists as an unusual trimer which is held together by long bridging interactions between the copper atom in one molecule and one of the hydroxy oxygen atoms from the adjacent molecules. 

As with other first-row transition metals, copper complexes are not expected to be satisfactory singlet oxygen photogenerators, because of the rapid deactivation of excited states in the presence of partially filled d-orbitals. The exceptional case of the copper(II) benzochlorin iminium salt ((18), M = Cu) has already been referred to (Section 9.22.5.6) this showed bioactivity, although the nickel(II) complex ((18), M = Nin) was inactive.195... 

A still more complicated reaction is the chemiluminescent oxidation of sodium hydrogen sulfide, cysteine, and gluthathione by oxygen in the presence of heavy metal catalysts, especially copper ions 60>. When copper is used in the form of the tetrammin complex Cu(NH3) +, the chemiluminescence is due to excited-singlet oxygen when the catalyst is copper flavin mononucleotide (Cu—FMN), additional emission occurs from excited flavin mononucleotide. From absorption spectroscopic measurements J. Stauff and F. Nimmerfall60> concluded that the first reaction step consists in the addition of oxygen to the copper complex ... 

The reaction of binuclear copper complexes with oxygen as models for tyrosinase activity was also markedly accelerated by applying pressure (106408 ). Tyrosinase is a dinuclear copper protein which catalyses the hydroxylation of phenols. This reaction was first successfully modeled by Karlin and co-workers (109), who found that an intramolecular hydroxylation occurred when the binuclear Cu(I) complex of XYL-H was treated with oxygen (Scheme 5). 

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